Hybrid electric vehicles include both an engine and at least one electric motor to provide drive torque to the wheels. There are various types of hybrid electric vehicles. For example, “parallel” hybrid vehicles typically include clutches that selectively enable either or both the engine and the motor to provide drive torque. A “series” hybrid vehicle typically includes an electric motor that is always driveably connected to the road wheels, and an engine that is not mechanically connected to the wheels. In other words, the engine does not provide any of the torque required to propel the vehicle. Rather, in a “series” hybrid vehicle, the engine powers a generator to produce electrical energy that is stored in the battery and/or used by the motor.
Various vehicles can include an overdrive gear selection enabling torque to be transmitted through an overdrive shaft. If an overdrive is provided in a hybrid electric vehicle, particular care must be taken to assure drivability is met while transitioning into and out of an overdrive mode. Due to the torque paths changing directions when entering and exiting overdrive mode, control of the engine and motor in the hybrid vehicle should be swift and accurate to ensure a smooth transition into and out of the overdrive mode.